This proposal requests continued support for a program of empirical and theoretical research on the perception, analysis, and synthesis of speech and the role of the lexicon in speech perception and auditory word recognition. The major goal of this project is to seek a better understanding of the earliest stages of speech processing. We are interested in how the initial acoustic-phonetic information in the speech waveform interacts with other sources of knowledge to support spoken language understanding. The proposed research will involve behavioral studies, computational analyses using large computerized databases, and simulation and modeling techniques to gain new knowledge about the perceptual and cognitive processes used by human listeners in perceiving phonemes, syllables, words, sentences, and passages of connected fluent speech. The proposed studies are divided into three major projects: (1) perception of synthetic speech generated by rule; (2) auditory word recognition and the lexicon; and (3)contextual variability in speech. From these projects we hope to learn more about how speech signals are processed by the nervous system and how the earliest stages of speech perception are interfaced to some of the more abstract linguistic and cognitive processes involved in spoken language understanding. The findings from this research have implications for normal and pathological language functioning as well as the diagnosis and treatment of communicative disorders involving the perceptual and cognitive processing of speech in adults and children.